Gas pressure blasting device



June 19, 1956 E. c. FlLsTRUP GAS PRESSURE BLASTING DEVICE Filed March 16, 1951 2,150,885 Gas PRESSURE BEASTING DEVICE Edward C. Filstrup, St. Joseph, Mich.,Y assigner to. Armastrong Coalbreak Company, Benton Harbor, Mich., a corporation of Michigan Application March 16,` 1951, Serial No. 215,974

6 Claims. (.CL 102-25) This invention relates to improvements in gas pressure blasting devices. More particularly the. invention relates to a device adapted to be charged with and to confine a charge of gas at high pressure and provided with means operating automatically when the pressure of the gas reaches a predetermined value to permit a certain and instantaneous discharge of the gas through outlet passages therein. Devices of this character are commonly used: in mining coal, being inserted in a drill hole in the face of the coal'v andv being adapted, upon. the instantaneous release of gas at high pressure, to break down. the coal around theV drill hole within which. the device is mounted.

In the use of devices of this character,` difficultyv has been. experienced heretofore by reason of the' development of detrimental, high temperature conditionsA incident to repeated or continued usage of the. shell. The high temperature condition has been such as to injure the device, as by enlarging they size of discharge ports, or the. like. A high temperature condition adjacent the discharge outlets may create a safety hazard inasmuch as tests reveal that, after a repeated. number of successive operations, the discharge of gas may be: accompanied by the emission of sparks. Another disadvantage. of^ the tendency of the device to heat is that. the device, when so heated, is diicult to handle manually.

Therefore, it is one of the primary objects of this invention to provide a device with novel protective cool.- ing means for preventing development of excessive ternperature conditions at parts of the device which. are liable to injury or damage. by such temperature conditions or at parts where high temperature. conditions would. create a safetyv hazard in the use of the. blasting device.

A further object of they invention is to provide a device of this character with a novel, simple anddnexpensive valve.

A further object is to provide av novel, simple and highly eflcient blasting device which is easy to use, and simple to operate and to condition fori operation.

Other objects will be apparent. from the. following speciication.

In the. drawing.:

Fig. 1 is anaxial sectional View of the device in its charging position.

Fig. 2 is an axial sectional viewy of the device in its discharging position.

Fig. 3 is an enlarged axial detail sectional View.v illustrating the connectiony of the cooling tube to the cartridge at the inletjport of the. device.

Fig. 4 is a fragmentary detail View illustrating: a modified embodiment of the invention.

Referring to the drawing -which illustrates thepreferred embodiment of the invention, the numeral designates an elongated tubular rigid body formed of steel having a thick wall and capable of withstanding high gas pressures in the order of 15,000 to 20,000 pounds per square inch. This tube may be of any length desired, for example, it may be from a'l'ength'of four feet to CTI Patented June 19,v 1956 a length of ten feet or more. In usual practice the diameter of the tube will range from two to` three inches, although this tube. size is stated as illustrative and is. not intended to. be limiting.

@ne end of the tubey 10 is internally screw-threaded at 12 to receive an end member 14, here illustrated as having a cup-shaped externally screw-threaded flange portion 16. One of the parts 10 and 14, here illustrated as the cylindrical Wall 16 of the end 14, has a circumferential groove adapted. for theV reception of a resilient annular sealingmember 18 which may be'` of the type commonly known in the art as: an. i3-ring. The seal 18 is of such character that it tends, to be deformed by pressure, so that the greater the pressure the greater will be the deforming and sealing action ofl the O-ring. The rear head 14 preferably has a shoulder 20 against which the rear endl of the tube 10 abuts.

A reducedA diameter externally screw-thrcaded endportion 22' is preferably formedy on the part. 14, said part 22 preferably having a coarse fast external screw-thread 24 formed therein and' having threaded engagement with an. annular internally screw-threaded wall 26 formed at one end of aprotective tube 28. The tube 28 will preferably be provided with an inwardly projecting or annular endflange 30.

The rear headl or'endmembers. 14' has` a bore 32 extend'- ing substantially axially therethrough at its forward end and. terminating ina, screw-threaded bore; portion 34' at its foremost part., Intermediate the longitudinal dimen* sion or thickness ofv the part 14, the bore 321 is enlarged to deiine a shoulder 36. The rear end of the enlarged bore portion is screw-threaded atv 3S'. A tubular fitting 4.0 tits snugly Within' the reduced bore portion 32y and has4 an enlarged frusto-conical tapered head 42 which seats. against the shoulder 36 and presents its frustoconical. surface 42 rearwardly.

A. metal' tube 44,.prefcrably a thick walled copperv tube, capable of' withstanding very high pressures., extends through the central opening in the restricted flange portion 30 with clearance, and its frontk end is a-red at L56 to tapered form having continuous bearing engagement with the tapered head 4Z of the fitting 4i?. A tubular member 48 having a bore axially therethrough teV receive the tube 44'v with clearance is externally screw-threaded to engage the screw thread 38 of the head 14. The tting 43 has a frusto-conical or ilaring mouth S0l which serves to press the end portion 46 of the tube into the flaring shape Shown. TheA arrangement is such that an effective gas-tight sealv is provided between the tube 4d and the fitting 40. The ltting 40 has an axial bore 52r which communicates withA the bore of the tubey 44;

A iitting 54 hasV anV externally screw-threaded' end portion which has threaded engagement in the part 34, of the head of the bore 14. The iitting 54 has a bore S6 extending continuously therethrough and also is prefer'- ablyA providedV with one or more lateral ports 58 which open the bore S6 of the fitting 54v into communication with the interior of the tube 10' around the tting 54. The front end ofthe tting 54 is externally'screw=threaded and mounts an internally screw-threaded nut 60' havingV an annular ange 62' at its front end'. The bore gti of the fitting7 54' is enlarged at 64 adjacent its front end and is adapted to receive the rear end of a tube 6.6. An annular retainer 6h encircles the end of the tube 66 and is. pressedl by the nut ii'ange 62 in. longitudinal direction against a flared portion of the socket of the tting 54 whereby said part 68 is deformed radially inwardly and caused to t into the tube 66. to anchor the same firmly in longitudinally extending and centered relation to the tube 10; The tube 66 preferably extends substantially full length of the tube 1t), although it may termin-ate slightly short thereof as illustrated.

The front end of the tube 1G is preferably internally screw-threaded at 70 to receive a tubular adapter 72. The tubular adapter 72 has an intermediate portion of substantially the same diameter as the tube and reduced end portions. The reduced end portion 74 is externally screw-threaded to t in the screw-threaded portion 70 of the tube 10, with the end of the tube 10 preferably bearing against the shoulder between the parts 72 and 74 of the adapter. A leak seal is provided be tween the tube and the adapter part 74, preferably in the nature of an annular resilient sealing ring 76 seated in a circumferential groove of one of the parts and being of the character adapted to deform under pressure for the purpose of effecting a seal to prevent the leakage of gas therepast. The opposite reduced end portion 78 of the tubular adapter is externally screw-threaded at 80 and may likewise be provided with a circumferential groove to mount and receive an annular resilient sealing member or ring 82.

A tubular head 84 is internally screw-threaded at one end for screw-threaded engagement with the threads 88 of the adapter part 78. The head 84 is preferably of greater thickness than the body tube 10 as illustrated, and bears against the intermediate shoulder or enlarged part 72 of the adapter as shown. The joint between the adapter part 78 and the tube head 84 is rendered leakproof by the sealing member 82. In forwardly spaced relation to the front edge of the adapter 72, the tube 84 is preferably provided with a groove 86 which mounts the annular resilient sealing ring 88. The bore of the tubular head 84 is preferably reduced slightly forwardly of the groove 86 to define a narrow shoulder 90. A vent passage 92 opening to the exterior of the sleeve 84 may be formed adjacent to the shoulder 90 and at the large diameter side of said shoulder. In forwardly spaced relation to the shoulder 90, the sleeve 84 is provided with a plurality of large circumferentially spaced ports 94, here illustrated as inclined rearwardly and outwardly. It will be understood that the number of ports 94 may vary, but their number, size and arrangement is preferably such as to insure substantially instantaneous discharge of gas from the interior of the device when the ports 94 are opened. The head tube 84 is provided with a circumferential groove 96 forwardly of the ports 94, and this groove is designed to receive a resilient annular sealing ring 98. The front end portion of the head tube 84 is preferably provided with an enlarged bore portion defining a shoulder 10i), and part of this bore may be internally screw-threaded at 102 at its mouth.

A forward head or end member 104 has a large diameter bore 106 formed therein for the majorl part of its length, said bore being reduced at an intermediate part 108 thereof defining a shoulder 110, and said bore having a smaller front portion 112. The head 104 has screw-threaded engagement with the threads 182 of the head sleeve 84 and preferably abuts the shoulder 100 at its rear end. An effective seal is provided between the head 104 and the head tube 84 in the nature of an annular resilient sealing ring 114, here illustrated as being mounted in a circumferential groove formed in the outer surface of the rear end portion of the head 104. The front end portion 116 of the head 104 has a large diameter internally screw-threaded bore formed therein, and is provided with a pair of diametrically opposed large apertures 118 spaced from its end edge. An annular washer or plate 120 seats in the bore in the front end 116 of the device, the plate 120 having an aperture therethrough substantially equal in diameter to the diameter of the bore part 112 of the head and in register therewith. Against the plate 120 is adapted to seat a shear member 122 which is introduced into the device through the aligned openings 118 in the head and which spans the bore 112. This shear member will preferably constitute a nail although any other rod, sheet or bar of suitable size and strength may be employed.. The

size and strength of the shear member may vary as desired and will control the operating characteristics of the device as hereinafter explained.

The shear member 122 is normally clamped in position by an end plug member 124 having an axial passage 126 therethrough of a diameter equal to or preferably slightly larger than the diameter of the bore 112. The plug 124 is externally screw-threaded for detachable screw-threaded engagement in the end portion 116 of the head 104, and the front end portion 128 of the plug 124 is preferably enlarged and may be knurled to facilitate manual manipulation to tighten and loosen the plug 124. At its rear end the plug 124 is cup-shaped, being provided with an axial socket into which ts an annular member 130 having a cylindrical rearward projection 132 extending beyond the rear end of the plug 124. A snap ring 134 may serve as a means to lock the ring 130 within the socket of the plug 124 and to permit rotation of thc parts 124 and 139.

A sleeve valve 136 is slidable in the tubular head 84 between the positions illustrated in Figs. l and 2. As best illustrated in Fig. l, the sleeve is of a length to span the outlet passages 94 and also to span the groove 96 and terminates in rearwardly spaced relation to the outlets 94. The annular resilient sealing member 98 serves as a seal to prevent leakage around the righthand end portion of the sleeve 136. One end of the sleeve valvc 136, here illustrated as the left-hand end, has an annular wall 138, and this annular wall is provided with one or more large openings 140 extending therethrough, and also is provided with a central opening. An elongated valve stem 142 of a diameter having a snug sliding fit in the bore 112 of the head is mounted in the central opening in the end wall 138 of the valve sleeve 136. The valve stem 142 has an abutment or shoulder 144 adjacet one end and bearing against one surface of the sleeve valve end wall 138 inwardly of the apertures 140. The rear end portion 146 of the stem is preferably screwthreaded and has clearance within the opening in the wall 138. A nut 148 is threaded on the stem portion 146 and serves to secure the stem 142 to the sleeve valve 136. A slight clearance of the parts will be provided for purposes to be described, such that the sleeve valve may have a slight movement or tilting action relative to the stem 142. The stem 142 will be of such a length that, when the sleeve valve 136 spans and seals or closes both the outlet openings 94 and the groove 96, its front end will engage and bear against the shear member 122. One or more coil springs 150 preferably encircle the stem 142 bearing at their rear ends against the shoulder 144, and bearing at their front ends against an annular' plate 152 seated against the shoulder 110. The member 152 cooperates with the bore part 108 of the head 104 to define a groove within which one or more annular resilient sealing members 154 are received and conned in a manner to insure against leakage of gas under pressure around the plunger 142.

A follower sleeve 156 is positioned between the end of the part 78 of the adapter and the end of the sleeve valve 136. The follower sleeve 156 is of greater thickness at the end thereof facing the intake of the device than at its opposite end, and a shoulder 158 is formed in its outer periphery and is adapted to seat against the shoulder 90 to limit travel of the follower. The sleeve 156 has a limited amount of free play or tolerance in its t Within the tube head 84 for purposes to be dcscribed. It will be observed that the annular resilient sealing ring 88 prevents the leakage of gas under pressure lengthwise of the follower sleeve at its outer surface. Consequently, the follower sleeve is subject to the application of a greater effective force to move it to the right than the force exerted to move the same to the left. lt will be observed also that no seal is provided for the righthand end of the follower sleeve, that is, between the vents or outlets 92 and 94. At its right-hand end the follower sleeve 156 is reduced in diameterv externally to provide a comparatively narrow annular lip 160; The annular lip has a flat edge lying in a plane transverse of the sleeve, as here shown, and the end wall 138 against which it bears, as illustrated in Fig. 1, also is flat and extends transversely of the axis of the sleeve valve 136, but it will be understood that the abutting valve-defining surfaces rnay take any shape found suitable or desirable.

In the use of the device it is placed in a hole drilled in the face of the coal to be broken down, the device having installed therein a shear member 122. The shear member is installed very easily by simply inserting it through the openings 118 when the cap or plug 124 is loosened, and then tightening the plug. The shear member may take any form found suitable, and one common form which is particularly well suited for use in the device is a nail, such as an S-penny nail or a IO-penny nail. It will be understood thatV the line 44 is connected to a source of gas, preferably air under pressure, such as an air compressor, or an air supply system including one or more compressors and one or more receivers. The capacity of air pressure of the system should be in excess of the air pressure at which it is desired that the blasting device shall shoot or discharge. In use in coal mines where it is desirable to shoot at pressures ranging from 7,000 to 10,000 pounds per square inch, depending upon the structure of the coal and the conditions in the mine, the compressor or fluid supply systems should be capable of su-pplying air at pressures at 10,000 to 12,000 pounds per square inch. After the shell has been inserted in the drill hole, the operators retire to a safe distance from the working face, and preferably behind a post or in a side passage, and the valve (not shown) for controlling the supply of gas through the inlet line 44 is opened to charge the device by filling its hollow body with high pressure air.

As the air pressure in the device increases, it applies a force upon the working mechanismof the device acting toward the right and entailing the application of pressure to tend to cause the plunger 142 to shear the member 122. It will be apparent that the pressure in the device is uniform throughout, and, in this connection, it will be observed that the ports 140 permit free passage of gas through the device so that the pressure in the device at the right of the sleeve valve 136 is equal to the pressure in the remaining portions of the device. This results in the application of force tending to shear the member 122 which is of a value determined by the cross-sectional area of the aperture 112 multiplied by the pressure of the charge within the container. This pressure is supplemented by the force acting toward the right, as viewed in the drawing, equal to the difference in the force applied at the opposite ends of the follower sleeve 156. Actually, the value of this force is equal to the area of the shoulder 158 of the follower sleeve 156 multiplied by the charging pressure. Inasmuch as the large area end of the follower sleeve is located at the left, the pressure effective upon the follower sleeve serves to move it toward the right, that is, toward the sleeve valve 136, and this force adds to the force acting upon the end of the stem 142.

When the sum of the two effective forces is sufficient to cause the plunger 142 to shear the member 122, the valve sleeve 136 shifts toward the right to the position illustratcd in Fig. 2, clearV of the ports 94. At the same time the pressure forces the follower sleeve 156 to move toward the right to the extent permitted by the spacing between the Shoulders 90 and 158, as viewed in Fig. l. When the shoulder 158 engages the shoulder 90, the sleeve 156 stops and, as seen in Fig. 2, this section occurs before the follower sleeve can move a distance sufficient to cover the ports 94. The ports 94 are thus left open and the gas of the charge is substantially instantaneously exhausted therethrough. The instantaneous discharge of the gas, when at a pressure in the range from 7,000 to 10,000 pounds, and assuming that the device has a chamber several inches in diameter and of a length of from four to ten feet, is effective to break down the coal around the device.

Since this device operates at high pressures, the retention of the gas charge is important. The use of O-rings or other seals at points 1,8, 76, 82, 114 and 154 insures that at points at which leakage` could be expected incident to joining or connection of parts, such leakage will be avoided. It is necessary, of course, that there shall be an effective seal associated with the sleeve valve 136. The O-ring 9S provides such a seal at one side of the ports 94. The O-ring SS provides such an effective seal at the other side of the ports 94. It will be observed, however, that inasmuch as the parts 136 and 156 are separate parts, any leakage of gas therebetween would be free to leak therearound either to the discharge ports 94 or to a vent port 92. In this connection it will be remembered that the sleeve valve 136 has av slight clearance in the bore of the head tube 84 and has a slight amount of play upon the stem 142. Under such circumstances the sleeve 136 is enabled to assume a position which will insure a continuous sealing engagement between the end face of the reduced diameter part and the surface of the end wall 138 of the valve sleeve. It has been found that a metalto-metal butt contact under these conditions, assuming that the faces contact each other continuously, will dene a valve preventing leakage of gas between the abutting surfaces. This is particularly true where the Wall thickness of the sleeve 156 at 160 is reduced, as to one-sixteenth of an inch or less. It will be understoodthat the thickness of the annular lip 160 preferably will be sufficient to enable it to withstand', without damage thereto or distortion, the force exerted upon the sleeve 156 at the discharge pressure, which force, as previously mentioned, is the product of the maximum charging pressure times the difference in area between the maximum outer diameter of the sleeve and the inner diameter of said lip. By this means only two annular resilient seals 8S and 98 are required adjacent to the discharge ports 94.

After the charge has been substantially completely evacuated, that is, after the gas pressure has reduced to a value equal to or slightly less than the value of the force exerted by the compressed springs 150, said springs will automatically return the valve sleeve 136 to the position illustrated in Fig. l. The broken parts of the shear member 122 can then easily be released, if necessary, by simply loosening the cap 124, and a new shear member 122 can be inserted and held in place by retightening the cap 124. The device is then ready for another operation. lt will be understood that the attendant will operate the control valve (not shown) to close that valve as soon as the blasting device discharges and will hold the control valve closed until the device is provided with a new shear pin and is inserted in the next drill hole to be blasted or shot.

The high gas pressures at which the device is` charged tend to have a heating effect thereon, and repeated discharge of the shell entails high frictional factors due to high velocity air ilow, and the device becomes heated incident to usage. The temperatures developed become quite high and are such as to tend to destroy the effectiveness and the life of the various annular resilient seals 18, 76, 82, S8, 98, 114 and 154 which are employed in the device. The temperatures may also be high enough to damage or injure some of the metal parts of the device, for example,`may cause undesired enlargement of the outlet ports 94 in a manner tending to weaken the construction or to render diilicult the maintaining of an effective seal. High temperatures also may cause the discharge of sparks at ports 94.

I have found that the use of the tube 66 is eective to hold the temperature at vital or critical parts of the device to values which are low enough to avoid injury and to provide safety of operation. The tube 66 extends substantially full length of the body tube or casing 10 and terminates adjacent to the adapter 72 and the valve control mechanism. As the air or other gas under high pressure is exhausted from the end of the tube 66 during the charging operation, it expands and exerts a cooling effect upon the right-hand end part of the device, including the adapter 72, the sleeve head 84, the valve sleeve 136, the follower sleeve 156, and the various annular resilient seals '76, 82, 8S, 98, 114 and 154 located at the head end of the device. It is also desirable, for the purpose of protecting the seal 118 and for cooling the rear end of the shell which is grasped by the worker in handling the device, to provide a cooling means at that end of the shell. For this purpose one or more ports 58 may be provided as shown, which permit the exhaust of air and the expansion of air at the left-hand end of the shell with consequent cooling effect.

Devices equipped with such cooling means have been found to possess longer effective life and to provide better performance characteristics than shells which are not provided with such cooling means, and it also has been found that there is less possibility that the workmen may suffer a burn in handling the device than is true with shells not so equipped. It will be understood that the cooling action is effective only at the localized areas mentioned and that high temperatures develop throughout the major portion of the length of the body tube 10. Those temperatures are not critical at that particular point, however, and when the shell is properly handled so as to be gripped only at its opposite ends, the worker can avoid injury due to heating of the intermediate part of the shell.

When the device discharges through the rearwardly outwardly inclined discharge ports 94, the action of the gas urges the device forwardly. This movement is stopped when the inner end of the drill hole is contacted, and the device is therefore subject to severe impact or shock. This shock imposes severe strain and stress upon the cooling tube, tending to fracture the tube or to pull the tube from the fitting 60. This can be obviated, if desired, by providing yielding means which cushions the shock of instantaneous deceleration. One such yielding means may consists of a section of elastic or extensible hose or conduit 67, such as a metal reinforced conduit formed of rubber or rubber-like material incorporated in tube 66, preferably adjacent to the fitting 60, as seen in Fig. 4. The extension of the elastic section absorbs the shock upon the tube when the device is shot.

While the preferred embodiment of the invention has been illustrated and described herein, it will be understood that changes in the construction may be made within the scope of the appended claims without departing from the spirit of the invention. It will also be underi stood that the terms forward or front, as used herein, refer to the right-hand portion of the item mentioned as viewed in the drawing; while the term rearWard, as used herein, refers to the left-hand portion of the item mentioned as it is viewed in the drawing.

I claim:

l. A gas pressure device comprising a hollow body having a lateral outlet and an end aperture, a shear member spanning said end aperture, a plunger slidable in said end aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a differential area follower sleeve having a limited pressure responsive movement in said body and normally abutting said sleeve valve, a pair of annular resilient sealing members carried by said body in longitudinally spaced relation at opposite sides of said outlet, said sleeve valve and follower sleeve having abutting end surfaces engaging to define a valve preventing leakage of gas therebetween.

2. A gas pressure device comprising a hollow body having a lateral outlet and an end aperture, a shear member spanning said end aperture, a plunger slidable in said end aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a differential area follower sleeve having a limited pressure responsive movement in said body and normally abutting said sleeve valve, a pair of annular resilient sealing members carried by said body in longitudinally spaced relation at opposite sides of said outlet, said sleeve valve and follower sleeve having abutting end surfaces engaging to define a valve preventing leakage of gas therebetween, said sleeve valve having limited play on said plunger to accommodate abutment of said last named valve-defining end surfaces.

3. A gas pressure device comprising a hollow body having a lateral outlet and an end aperture, a shear member spanning said end aperture, a plunger slidable in said end aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a differential area follower' sleeve having a limited pressure responsive movement in said body and normally abutting said sleeve valve, a pair of annular resilient sealing members carried by said body in longitudinally spaced relation at opposite sides of said outlet, said sleeve valve and follower sleeve having abutting end surfaces engaging to define a valve preventing leakage of gas therebetween, said sleeve valve having limited play on said plunger to accommodate abutment of said last named valve-defining end surfaces, each of said sleeve valve and follower sleeve having limited clcarance in said body.

4. A gas pressure device comprising a hollow body having a lateral outlet and an end aperture, a shear member spanning said end aperture, a plunger siidable in said end aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a differential area followersleeve having a limited pressure responsive movement in said body and normally abutting said sleeve valve, a pair of annular resilient sealing members carried by said body in longitudinally spaced relation at opposite sides of said outlet, said sleeve valve and follower sleeve having abutting end surfaces engaging to define a valve preventing leakage of gas therebetween, said follower sleeve having a reduced diameter end portion engaging said sleeve valve, said valve-defining surface being formed at the end of said reduced diameter portion.

5. A gas pressure blasting device comprising a hollow body having a lateral outlet and an end aperture, a shear member spanning said end aperture, a plunger slidable in said end aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a differential area follower sleeve having a limited pressure responsive movement in said body and normally abutting said sleeve valve, a pair of annular resilient sealing members carried by said body in longitudinally spaced relation at opposite sides of said outlet, said sleeve valve and follower sleeve having clearance in said body and cooperating valve defining abutting surfaces normally positioned between said resilient sealing members.

6. A gas pressure blasting device comprising a hollow body having a lateral outlet and an end aperture, a shear member carried by said body and spanning said end aperture, a plunger slidable in said aperture, an annular resilient sealing member encircling said plunger at said aperture, a sleeve valve carried by said plunger and adapted to span said outlet, a pressure responsive follower sleeve in said body, said sleeve and sleeve valve having abutting valve-defining surfaces, means limiting movement of said follower sleeve in said body, and longitudinally spaced sealing means encircling said sleeves and positioned at opposed sides of said outlet and of said valve-defining surfaces.

References Cited in the file of this patent UNTED STATES PATENTS 2,083,735 Noble June l5, 1937 2,120,034 Myers June 7, 1938 2,253,115 Ferrell et al. Aug. 19, 1941 2,502,694 Armstrong Apr. 4, 1950 

